Alternating current is electricity that flows first in one direction and then the other, in contrast to direct current which flows only in one direction. Some key developments in alternating current include William Stanley designing an efficient power transfer device in 1886 and contributions by Nikola Tesla and others. AC is commonly used today because it can be transformed to different voltages allowing power to be distributed over long distances more efficiently. The voltage and current values in an AC circuit are represented using root-mean-square values to average out the changing values. Components like resistors, capacitors, and inductors interact differently with alternating current compared to direct current due to properties like reactance.

1. Alternating CurrentAlternating CurrentAlternating CurrentAlternating Current

3. HHISTORY OF ALTERNATING CURRENTISTORY OF ALTERNATING CURRENT
William Stanley, Jr. designed one of the
first practical devices to transfer AC
power efficiently between isolated
circuits.
The AC power system used today
developed rapidly after 1886, and
included contributions by Nikola Tesla
and Carl Wilhelm Siemens.

4. WHAT IS ALTERNATING CURRENT ?WHAT IS ALTERNATING CURRENT ?
• Alternating current electricity is the type of electricity commonly used
in homes and businesses throughout the world.
• AC electricity is created by an AC electric generator, which
determines the frequency.
• An AC waveform can be sinusoidal, square, or saw tooth-shaped.
Some AC waveforms are irregular or complicated.

5. Alternating current flows first in one direction and then in
the other direction.

6. AAdvantagesdvantages
• The single greatest advantage of alternating current is that AC current can
be transformed and DC current cannot be transformed.
• It can be controlled by a wide range of components eg.resistors, capacitors
and inductors.
• This allows high-voltage electrical power to be distributed with smaller wires
and lower amperage.

7. DIRECT ALTERNATING

8. RMS VALUESRMS VALUES
• Since voltage and current are always changing we need some way of
averaging out their effect.
• We use R.M.S values (root-mean-square)
• The R.M.S values are the DC values which give the same average power
output

10. ACAC in capacitorsin capacitors
In an AC circuit, the current can continue to flow, as the plates become alternately
charged positively and negatively
For both AC and DC circuits, the voltage across the resistor is related to the current by
V=I.R
A similar relationship exists for a capacitor:

11. RReactanceeactance
• Reactance is a measure of how a capacitor can limit alternating current.
• It is similar to resistance but differs in that it is dependent on the
frequency of the ac supply.
• It also depends on the size of the capacitor.

12. IMPEDANCEIMPEDANCE

13. Ac In Inductors
.In an AC circuit, the current is always changing so the inductor is always
producing an opposing voltage so is always limiting the amount of current that
can flow
For both AC and DC circuits, the voltage across the resistor is related to the
current by V=IR
A similar relationship exists for an inductor

14. reactance
It measures how well an inductor can limit alternating current
It depends on the frequency of the ac supply.
It depends on the size of the inductor

15. IMPEDANCEIMPEDANCE

16. Phase relatIonshIpPhase relatIonshIp
The current in the circuit will always be in phase with VR

17. The voltage phases are not necessarily the same size,
but are always 90°out of phase.

18. Again the voltages may be different sizes but will always
be 90° out of phase

19. RLC CIRCUITSRLC CIRCUITS
The supply voltage is now found
by adding all 3 phases
together.
(VL and VC are combined into
one first)

20. RResonanceesonance
At resonance, VL=VC and
they cancel each other out.
So VS=VR and if VR is at max
then I is at max.

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